For conventional pivoted pick-up arms the current state of technology mandates the use of knife edge-, ball-, ball and cone-, unipivot bearings or a combination of any of these. One of the drawbacks of these bearing principles is that the inherent friction and therefore disturbances of the pick-up arm movement can only be reduced to a system immanent minimum. The disturbances are the consequence of a continuous alternation between static friction and sliding/rolling friction(“stick-slip” or “stiction” effect) while the pick-up arm is traversing the record forcing the cartridge to move in a jerky fashion, this being a detrimental influence on the fidelity of the cartridge's performance.
Additionally, the use of a bearing that rigidly couples the pick-up arm tube to the turntable (pick-up arm base, plinth, motor, platter) negatively affects the undisturbed tracking of the groove modulation. Disturbing parasitic resonances, i.e. excited by motor vibrations, air-or structureborne vibrations, are transmitted via the pick-up arm and it's armtube to the cartridge leading to an alteration aka distortion of the original signal. Likewise does the process of tracking the long-playing record (“LP”)-groove by the cartridge excite resonances in the pick-up arm and the turntable it is mounted on.
The option to dampen the so-called “tonearm-cartridge resonance” (typically between 7 Hz and 14 Hz) by means of a silicon oil damping trough and pin/paddle featured by many pick-up arms negatively affects the reproduction of the upper frequency range of the music signal, overdamping.
Another drawback of conventional pivoted pick-up arms is their sensitivity to shock-induced damage. Commonly used bearing cups made out of precious or semi-precious stone are very brittle and crack or break easily. Their counterparts, bearing pins or cones—as much as conventional ball bearings almost inescapably suffer some damage after exposure to a strong shock or unsuitably rough handling. The damage manifests itself in flattened or bent bearing pin tips, flat spots on balls, indentations on their counterpart ballraces, these damages leading to increased and uneven friction, substantially reducing the fidelity of the pick-up arm.
DE 22 60 855 C2 describes a pick-up arm that uses repelling magnets to carry the axial load of the moving assembly. This arrangement results in reduced friction when moving the pick-up arm(tube) around it's vertical axis only.
U.S. Pat. No. 4,121,837 describes a turntable whose pick-up arm is damped axially by an electromagnetic damping arrangement. To achieve this, the arm features an electrically conducting sickle-shaped element that is attached to the pick-up arm near the (conventional=friction charged) horizontal bearing point. The electrically conducting sickle element travels horizontally through a magnetic field generated by two permanent magnets. Any movement of the sickle-shaped element relative to the magnets results in an induction of eddy currents in the sickle-shaped element, the resulting magnetic field surrounding said element leads to a repelling force in relation to the field generated by the two permanent magnets. The opposing magnetic field restricts and dampens the movement of the sickle-shaped element. The drawbacks of such an arrangement are: a) the sickle-shaped element increases the effective mass, b) the sickle-shaped element is prone to resonances, it is effectively a resonating tongue, and c) the arm “sees” no damping of vibrations in the vertical plane, stemming from i.e. warped records or footfall.
U.S. Pat. No. 4,570,253 describes a pick-up arm system where the arm tube is suspended by two threads via a disc-shaped element, predominantly in the vertical plane through a viscous fluid. The upper ends of the threads are attached to the pick-up arm base at two separate points near the pivot revolving point, the lower ends of the threads are attached to separate adjacent holes in the disc-shaped connecting element which rigidly holds the arm tube. This disc-shaped element is immersed in a cup filled with a viscous fluid. This arrangement is supposed to reduce the skating force that is a result of the friction of the “needle” travelling through the groove and the offset angle of the tonearm resulting in a force vector effectively pulling the arm towards the center of the record. It's disadvantage is that tilting motions and resonances along the pick-up arm's vertical axis are damped by the viscous fluid exclusively. Undesirable and inescapable shifts of the assembly's pivot while the arm is in operation are damped by the fluid only, the stabilizing effect defined by the viscosity of the fluid. Altering the damping characteristic is possible only through a time consuming exchange for another fluid of different viscosity.
The closest current state of technology is described by DE 30 02 013 C2. A thread (bearing) forms the equivalent of the vertical axis of a pick-up arm tube bearing housing that is stabilized by cylindrical permanent magnets of opposite polarity in the vertical direction attracting each other, allowing rotation solely in the horizontal plane, stabilizing the bearing housing axially only. The permanent magnets that are situated above the armtube, carrying the weight of the whole bearing housing, armtube and counterweight. The gap between the magnets is determined by the length of a thread under tension, located below the bearing housing/armtube assembly, connected to both the pick-up arm chassis and the bearing housing/armtube assembly. The permanent magnets are set in vertically oriented tubes, the upper of which is rigidly connected to the pick-up arm chassis. The arm tube is coupled to the bearing assembly via conventional, needle and cup-, ball- or knife edge bearings. The disadvantage of such arrangement lies in the fact that the pick-up arm still features a conventional pivot for the vertical movement of the armtube displaying a certain frictional resistance in operation. The arrangement predominantly aims at the compensation of the “skating effect”. The permanent magnets in their tube shaped setting have a stabilizing function in the vertical axis only. Any vertical arm tube movement is neither stabilized nor damped.
Starting out from this state of technology it is the task/aim of the presented invention to provide a pick-up arm system that features extremely low, close to zero, friction and variable damping of arm movement in all three planes, combined with very low sensitivity to shock induced bearing damage.
The task is met by the characteristics/features of claim 1.
According to the invention, a torsion element, in this case a high tensile strength, non elastic thread (particularly a multifilament) is running congruent to the vertical axis of rotation and through the horizontal pivot inside the receiving element of the arm tube. The lower end of the torsion element is set into a permanent magnet which itself is set into the receiving element for the tonearm tube. The upper end of the torsion element is fixed to the upper extension of the pick-up arm chassis. Torsion element materials that can be used alternatively are: very thin steel wire or similar materials that combine high tensile strength and very low stretch.
A pick-up arm system, consisting of pick-up arm chassis, pick-up arm tube and suspension bearing is sometimes referred to as tonearm. In accordance with this invention, “tonearm” and “pick-up arm system” are to be regarded as the same.
In accordance with this invention, “tonearm tube” describes any type of pick-up arm-tube/stick/wand. According to the invention this means in particular not only a tonearm featuring a central longitudinal hole but also one that has a groove/longitudinal cutout rendering the longitudinal hole obsolete. Furthermore, according to this invention the term tonearm tube means a tonearm(tube) that has no hole and/or cutout at all, effectively a rod.
The upper permanent magnet, cylindrical in shape and extremely strong has a vertical extension that is less than the diameter of the tonearm tube receiving element, whereby the bottom of the permanent magnet is essentially flush with or does not extend beyond the bottom of the tonearm receiving element. The shape of the bottom side of the permanent magnet can be chosen freely, preferable are a planar, spherical segment or cylinder segment shape. To take up or fixate the torsion element, the magnet has a centerhole in which the torsion element is set without play/slack. Alternatively, the torsion element can be led through a centrally drilled pole piece made out of a high permeability material, whereby the thickness of the pole piece is chosen to provide enough room to fixate the torsion element, particularly for a countersunken hole to accept the knot. The permanent magnets consist of strongly magnetizing materials, particularly Neodym-Iron-Boron—or Samarium-Cobalt—alloys. Combining the two is feasible too.
Perpendicular underneath the permanent magnet in the pick-up arm receiving tube a second permanent magnet of opposite polarity is fixed to the lower extension of the pick-up arm chassis.
According to the invention, the torsion element facilitates three degrees of freedom(of movement). The pick-up arm receiving element and therefore the pick-up arm tube is suspended by a vertical thread which, to allow for rotation in the horizontal plane, needs to be slightly twisted only. When the arm is moved up and down, the thread is just being bent at the lower end(inside the pick-up arm tube receiving element) where it exits the magnet/pole piece. Rotation of the armwand around it's longitudinal axis is prevented since the center of gravity of the counterweight/pick-up arm tube/cartridge assembly is located below the vertical bearing(thread bending) point. This results in a steady condition in regard to the longitudinal axis of the pick-up arm tube.
While coupling the pick-up arm tube receiving element to the pick-up arm chassis without slack(or bearing play) the high inherent damping of the torsion element surpresses the excitement of mechanical resonances in the pick-up arm chassis by the cartridge. The length of the torsion element (between the upper fixing and the lower exit point) also ensures the suppression of footfall induced pick-up arm chassis vibrations relayed to the pick-up arm tube, meaning, parasitic vibrations are not added to the original signal(as encoded in the groove's modulation), maintaining it's fidelity.
The bearing friction is equal to the torsional friction of the torsion element, far lower(factor 10–1000) than the friction of bearing types used in conventional pick-up arm designs, i.e. unipivot-, knife edge- or ball bearings.
The movement of the pick-up arm tube in relation to all three degrees of freedom is damped through the induction of eddy current in the aluminum settings that hold the magnets(eddy current brake principle). Any change of the position of the pick-up arm tube results in an alteration of the flux line geometry of the magnetic field surrounding the two magnets. The strength of the eddy currents induced in the aluminum magnet settings is increasing proportionally to the velocity of the pick-up arm tube, independent of what is causing the movement/vibration, be it the cartridge or the turntable.
The permanent magnets in the pick-up arm tube and the pick-up arm chassis serve the function of stabilizers and dampers in all dimensions, including sideways, back and forth, or up and down. Additionally, the torsion element strongly inhibits the excitement/occurrence of pick-up arm tube resonances resulting from footfall or airborne resonances. Furthermore, the distance between the magnet in the pick-up arm wand and the perpendicular, pick-up arm chassis mounted counterpart is variable and facilitates the adjustment of the rigidity and the damping properties of this “quasi”-rigid bearing.
The torsion element runs through a vertical hole in the receiving element for the pick-up arm, the diameter of said hole chosen to give the torsion element enough freedom of movement to allow for the unimpaired tracking of even the most warped records, meaning the torsion element does not touch the upper rim of the hole while playing warped records. Connected to or sliding on to the rear end or stub of the pick-up arm receiving element is a counterweight, the center of gravity of which is located below the upper end of said hole.
This hole, effectively a well, can be filled with silicon oil. This yields the advantage of immersing the torsion element in silicon oil for approximately one third of it's length, additionally damping the transmission of vibrations stemming from the pick-up arm chassis via the torsion element to the pick-up arm tube. The dimensions of this “oil well” and the choice of silicon fluid of suitable viscosity exclude the possibility of overdamping the pick-up arm/cartridge resonance. Since the torsion element is running vertically through the “oil well”, the silicon oil has a neglectable amount of damping in the horizontal plane regards to horizontal pick-up arm tube movement.
Optionally the pick-up arm receiving element and tube can be made out of a single piece of wood or a sandwich of several woods, the woods are characterized by high bending strength combined with high internal damping. Particularly suitable are ebony, jacaranda, acacia, cocobolo and bamboo, and many others are suitable too. The inner diameter or bore hole of the pick-up arm tube is chosen to be just large enough to take up the pick-up arm wiring, preventing microphony effects and the excitement of the enclosed column of air (pipe resonances).
Several advantageous features are described in the remaining sub-claims; the invention is being described using an executed sample and the following schematic drawings: